Alignment films are arranged on an array substrate and a color filer substrate of a thin film transistor liquid crystal display (TFT-LCD) respectively, and grooves are arranged on each alignment film in a predetermined direction and configured for causing liquid crystal molecules to be arranged in the direction of the grooves in a condition that the liquid crystal molecules are not affected by an electric field. The alignment film having an alignment function is generally formed by a polyimide (PI) film in a process of: rubbing a PI film coated and solidified on a glass substrate by a roller being wrapped up by rubbing cloth, so as to form the grooves on a surface of the PI film in the predetermined direction.
During the process of forming the alignment film, since the rubbing cloth may have defect such as uneven width, foreign substances being adhered to a surface, an affection by impurities during the process of rubbing for forming the grooves or etc., the grooves on the alignment film formed by such processes may have a direction, a shape, a depth and etc. that deviate from a desired direction, a desired shape, a desired depth and etc. respectively, namely a rubbing mura is generated, so that the alignment performance is adversely affected. Thus, it is necessary to detect whether there is a defect in the grooves on the alignment film after the alignment film has been formed.
In related art, it generally determines whether there is a defect in the grooves on the alignment film by a method including following steps.
Water vapor is sprayed to a surface of the alignment film on the glass substrate by a vapor spray nozzle which is typically hold by an operator manually, so as to form water particles on surfaces of the grooves. Meanwhile, a region of the alignment film where the water vapor is sprayed by an intense light is irradiated, so as to determine whether there is a defect in the grooves on the alignment film manually (a diffused reflection may occur at a position of the defect in the grooves when the light ray is transmitted through the position) by viewing the grooves irradiated by the intense light (it typically generates a bright line, i.e. a line mura).
When the defect in the grooves on the alignment film is detected, the position of the defect in the grooves is generally measured by a ruler. A measurement value is manually converted to an approximate position of a defect in the rubbing cloth corresponding to the position of the defect in the grooves, and the defect in the rubbing cloth is repaired. Then the PI film is rubbed again and it detects whether there still exists the defect in the grooves on the alignment film by the above vapor detection method, so as to determine whether the defect in the rubbing cloth is eliminated.
However, the above vapor detection method has following disadvantages.
Firstly, the water vapor is sprayed and adhered to the glass substrate and the surface of the alignment film. Thus, during the process of forming the water droplets, some of the formed water droplets continue to disappear due to facts of air movement, evaporation and so on, so that a period of spraying the vapor for the detection is prolonged, and the efficiency is lowered.
Secondly, the efficiency of the above method for detecting whether there is the defect in the grooves on the alignment film is low because it is implemented manually. In addition, the credibility of the detection result may be low because different operators may have different standards for the detection by their eyes respectively.
Thirdly, when the glass substrate and the alignment film are large, some regions in the glass substrate and the alignment film may be unreachable by the vapor spray nozzle hold by the operator, so that the defect in grooves in these regions of the alignment film is undetectable.
Fourthly, the vapor spray nozzle is typically in direct connection with a water tank being heated. As a result, when a water level in the tank is high, it is possible that some water droplets in the tank are transmitted to the vapor spray nozzle and sprayed to the alignment film, and thus the subsequent process is adversely affected.
Fifthly, the grooves on the alignment film are required to be smaller as a capability for detecting the alignment grooves in the TFT LCD is becoming stronger. Since an evenness of the water droplets formed on the surfaces of the glass substrate and the alignment film is poor and observation limitation on human eyes, the above vapor detection method cannot satisfy the requirement of detecting the defect in the grooves on the alignment film of the TFT LCD which has a strong detection capability for detecting the alignment grooves.
Furthermore, the above vapor detection method is implemented manually, so that the position of the defect in the rubbing cloth generally cannot be accurately determined by the manual computation, and thus it is impossible that the defect in the rubbing cloth is eliminated by one-time positioning and repairing. As a result, the above process has to be repeated several times. If the defect in the rubbing cloth still has not been eliminated by repeating the above process several times, the rubbing cloth has to be replaced by a new one, which is expensive and laborious, and also reduce utilization of the production line.